Add metrics when the connections limit is set

[cescoffier]

When the HTTP connection limit is set:

• expose a new gauge with the max number of connections
• expose a new gauge with the current number of connections
• expose a new counter with the number of rejected connections

[quarkus-bot]

/cc @brunobat (micrometer), @ebullient (micrometer)

[brunobat]

I imagine the maxConnections is the constant you were talking in the morning...
Do you thing you can add a test?

[cescoffier]

@brunobat I can try, but it's tricky. Our test frameworks do not use persistent connections, so we will have only one connection reported. If I want to test the number of rejections, I would need to create many connections and execute them concurrently. This is the best recipe for flakiness, as the level of concurrency and execution depends on the machine executing.

I manually tested it locally because browsers, unlike our test framework, use persistent connections (and the dev UI is opening 5 connections! (I need to investigate that with @phillip-kruger when he is back)).

[brunobat]

Ok @cescoffier. Worst case, a test with a single connection is fine because if we test the metric doesn't go away accidentally it's something already. If you add an issue for the more complex work, I'm fine merging this now.

[cescoffier]

@brunobat I accepted the challenge and implemented a test.
It should be fine on most systems....

[brunobat]

thanks @cescoffier

[quarkus-bot]

Failing Jobs - Building 31474fd

Status	Name	Step	Failures	Logs	Raw logs	Build scan
✔️	JVM Tests - JDK 17					🔍
✖	JVM Tests - JDK 21	Build	Failures	Logs	Raw logs	🔍

Full information is available in the Build summary check run.
You can consult the Develocity build scans.

Failures

⚙️ JVM Tests - JDK 21 #

- Failing: integration-tests/elasticsearch-java-client integration-tests/elasticsearch-rest-client integration-tests/hibernate-orm-tenancy/connection-resolver and 3 more

📦 integration-tests/elasticsearch-java-client

✖ Failed to execute goal io.fabric8:docker-maven-plugin:0.43.4:start (docker-start) on project quarkus-integration-test-elasticsearch-java-client: I/O Error

📦 integration-tests/elasticsearch-rest-client

✖ Failed to execute goal io.fabric8:docker-maven-plugin:0.43.4:start (docker-start) on project quarkus-integration-test-elasticsearch-rest-client: I/O Error

📦 integration-tests/hibernate-orm-tenancy/connection-resolver

✖ io.quarkus.it.hibernate.multitenancy.inventory.HibernateNamedPersistenceUnitTest.testGetPlanesDefaultTenant line 21 - More details - Source on GitHub

java.lang.AssertionError: 
1 expectation failed.
Expected status code is <200> but was <500>.

	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
	at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:73)

✖ io.quarkus.it.hibernate.multitenancy.inventory.HibernateNamedPersistenceUnitTest.testGetPlanesTenantMycompany line 31 - More details - Source on GitHub

java.lang.AssertionError: 
1 expectation failed.
Expected status code is <200> but was <500>.

	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
	at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:73)

📦 integration-tests/hibernate-search-orm-elasticsearch-tenancy

✖ Failed to execute goal io.fabric8:docker-maven-plugin:0.43.4:start (docker-start) on project quarkus-integration-test-hibernate-search-orm-elasticsearch-tenancy: I/O Error

📦 integration-tests/hibernate-search-orm-opensearch

✖ io.quarkus.it.hibernate.search.orm.opensearch.devservices.HibernateSearchOpenSearchDevServicesEnabledImplicitlyTest.testDevServicesProperties - More details - Source on GitHub

java.lang.RuntimeException: 
java.lang.RuntimeException: io.quarkus.builder.BuildException: Build failure: Build failed due to errors
	[error]: Build step io.quarkus.elasticsearch.restclient.common.deployment.DevServicesElasticsearchProcessor#startElasticsearchDevService threw an exception: java.lang.RuntimeException: org.testcontainers.containers.ContainerLaunchException: Container startup failed for image docker.io/opensearchproject/opensearch:2.9.0
	at io.quarkus.elasticsearch.restclient.common.deployment.DevServicesElasticsearchProcessor.startElasticsearchDevService(DevServicesElasticsearchProcessor.java:108)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.quarkus.deployment.ExtensionLoader$3.execute(ExtensionLoader.java:849)
	at io.quarkus.builder.BuildContext.run(BuildContext.java:256)

📦 integration-tests/logging-gelf

✖ Failed to execute goal io.fabric8:docker-maven-plugin:0.43.4:start (docker-start) on project quarkus-integration-test-logging-gelf: I/O Error